The protective shield of a human rights treaty in principle only works once it has entered into force. But what about the frequent problem of human rights violations that occurred or started before that time; can one complain about those on the international level? In other words, what are the limitations of the ratione temporis jurisdiction of supervisory human rights mechanisms? This article explores this question in the context of general public international law through a case study of the European Convention on Human Rights. It argues that the European case law's variations on principles of international law can be explained by the special nature of human rights treaties.